Process for preparing ceramic powders in the presence of a source of carbon, powders thus obtained and their use

ABSTRACT

A method for preparing ceramic powders in the presence of a carbon powder including a step which consists in homogenizing a mixture of particles capable of resulting in a ceramic by heat treatment. Said method can be carried out in the presence of an accelerated solvent and provides, at reduced energy consumption, carbon-coated ceramic powders and then ceramics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/857,740, filed on Apr. 5, 2013, which is a divisional of U.S.application Ser. No. 12/728,991, filed on Mar. 22, 2010, now U.S. Pat.No. 8,425,976, which is a continuation of U.S. application Ser. No.10/516,242, filed Sep. 30, 2005, now abandoned, which is a nationalstage application of International Application No. PCT/CA2003/00795,filed May 27, 2003, and claims priority to Canadian Application No.2,389,555, filed May 30, 2002. The entire contents of each of U.S.application Ser. No. 13/857,740, U.S. application Ser. No. 12/728,991,U.S. application Ser. No. 10/516,242, International Application No.PCT/CA2003/00795, and Canadian Application No. 2,389,555 are herebyincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a process for preparing ceramic powdersin the presence carbon. This process is particularly advantageous forthe preparation of ceramic powders whose average size if of the order ofa nanometer, and as a preliminary step for the preparation of ceramics.

The present invention also concerns the ceramic powders and the ceramicsobtained by these processes, for example conducting ceramics containingresidual carbon and their use in industry.

STATE OF TECHNIQUE

Any product that is manufactured by heat treatment, for example fromclays, sands, feldspaths and/or chalks is generally called ceramics.

Within the framework of the present invention, a ceramic powderdesignates any mixture of particles capable of giving a ceramic productafter heat treatment.

As mentioned for example in part 3 of the “Grand Larousse Universel”published by Actualia, the ceramics, in plural form, are all themanufactured metals or all the products that are chemically inorganic,except for the metals and their alloys, and that are generally obtained,by high temperature treatments.

Scientific literature mentions different types of ceramics, for exampletraditional ceramics such as glasses, hydraulic binders (cement, lime)and sheet iron enamels. The other ceramics are usually classified in twocategories, according to the nature of the cooked body used for theirpreparation.

Ceramics are first concerned with porous type products characterized byan earthy fracture and a permeable body, for example permeable bodystructural clay products which are more or less colored in red with ironoxide such as terra-cotta, varnished structural clay products,stanniferous faience, high temperature resistant refractory products,white and fine permeable bodies such as fine faience.

Ceramics are also concerned with impermeable ceramic products such asstoneware, porcelains with hard bodies, and sanitary porcelains.

Part 3 of the “Grand Larousse Universel” edited by Actualia alsomentions new ceramics that correspond to a large number of categoriesincluding oxides, carbides, nitrides, borides and silicides. Theseproducts mainly obtained from powders are commonly referred to asfritted products. This category covers compounds having a binary type ofphysico-chemical structure, while the silicated traditional ceramicscorrespond for their part, to a mixture of oxides in variousproportions.

Ceramics of technical types are used in the high technology sectors,such as nuclear industry, aeronautics, computer science and electronics.

Recent advances in the technology of materials have widened the field ofapplication of ceramics to new applications based on electrical,magnetic, optical, piezoelectric, mechanical and nuclear properties, andwhich exploit the nature of the raw materials used, whether we areconcerned with oxides or non-oxides such as carbides or nitrides,products of the chemical industry.

Formerly, clay and hydrated alumina silicate (SiO₂AlO₃H₂O) made up mostof the raw material used for the manufacture of decorative ceramics,tiles, sanitary equipment and some refractory products.

Since then, the use of other natural or synthetic raw materials of thefritted alumina type, silica, silico-aluminous magnesium compounds(cordierite, mullite, steatite) was at the origin of the development ofso called technical ceramics.

Thus, the use of alkali-earth metals, carbon as well as nitrogen, hasmade it possible to develop new phases such as oxinitrides, sialons, andcarbides that are used in the state-of-the art ceramics.

The concept of raw material also called mixture of precursors hastherefore widened with time. It relates to materials having undergone anextremely complex preparation.

-   -   powders (oxides, nitrides, carbides . . . ): thanks to new        preparation processes, powders with controlled grading and of        high chemical purity are obtained; the final product is then        obtained by shaping followed by heat treatment;    -   monocrystalline short fibers: short fibers of the order of a few        fractions of millimeter are dispersed in a matrix that may be        organic, metallic or ceramic;    -   silicon carbide wiskers are used for the production of composite        materials with high mechanical resistance;    -   organo-metallic precursors: by thermolysis, some complex organic        molecules give rise to carbides or nitrides (SiC, Si₃N₄ . . . )        used for example in the refractory industry to develop a product        with high technicality; finally, the chemical industry has        provided ceramists with molecules acting as binders or        plasticizers (polyvinyl alcohol, carboxymethyl cellulose,        alginate, wax . . . ) allowing access to new shaping processes,        such as dry pressing, thermoplastic injection, and banded        casting.

The recently developed ceramics are often qualified as fine or technicalceramics. This qualification is used because the raw material is amineral powder shaped to produce the object, and a heat treatment isrequired to give it the desired characteristics.

Ceramics are poly-crystalline, polyphased materials in which the finalproperties of the product are conditioned by the intrinsic properties ofthe components. Thus, a combination of conducting grains and ofinsulating joints is essential for the properties associated with manyceramic components that can be used in the field of electronics.

The development of specific microstructures for example those includingzirconia and reinforcing fiber, gives to the ceramics a rupture stressthat compares that of metals, while preserving a clearly superiortemperature resistance.

Light ceramics have been found to provide ideal materials in the fieldof aeronautics. On the other hand, the development of ceramics having agiven porosity permits the manufacture of membranes that are highlyuseful in the environmental techniques and in the agri-food industry.The use of nanometric powders and of materials with compositiongradients allows on its part to prepare new ceramic products.

Among the recently developed processes for the preparation of newceramics, banded casting, isostatic pressing and injection or extrusionmolding may for example be mentioned.

Moreover, the plasticity that is required for the operation of shapingthe ceramics is made possible by the use of binders or plasticizers, oforganic products such as waxes, cellulose or acrylic compounds, in theprocesses of preparing ceramics.

Recently, coagulation techniques (sol-gel) that are extremely easy touse were developed.

Finally, ceramics have the advantage of being able to be prepared in theform of thin or thick layers, and of thereby using only limitedquantities of raw materials.

As used as coating, ceramics act in protecting against wear, corrosionand/or heat for example. With their specificity as electrochemicalsensors, ferroelectric memories, and/or transparent electrodes, they canalso be integrated in more complex systems, such as those found inelectronics and microengineering.

Technical ceramics are used in all the important fields of theindustrial activity as was mentioned in the publication “LesApplications”, extracted from the document “Les Céramiques”, edited byLe Centre Européen de la Céramique, Limoges, France.

In spite of a high level of performance associated with ceramics, theirdevelopment is still relatively limited, because of the fact that theprocesses generally used for manufacturing ceramics are long andcomplex. Another one of the numerous limiting factors in the developmentof ceramics resides in the high energy cost that is associated withtheir preparation. There was therefore a need for the development of newprocesses for preparing ceramics with improved productivity andprofitability.

IN THE DRAWINGS

FIG. 1: illustrates a conventional process for preparing ceramics, thisprocess utilizes a succession of heat treatments and grindings of heldback particles to produce the ceramic powder.

FIG. 2: illustrates an embodiment of the process according to theinvention allowing an accelerated preparation of ceramic product inwhich the powder undergoes a limited number of sequences.

SUMMARY OF THE INVENTION

The present invention relates to a process for preparing a ceramicpowder in the presence of a carbon powder, including at least one stepof homogenizing the mixture of particles capable of resulting in aceramic product by heat treatment. This accelerated process makes itpossible to obtain, at a reduced energy cost, ceramic powders andceramics.

DESCRIPTION OF THE INVENTION

A first object of the present invention resides in a process forpreparing a ceramic powder from a mixture of precursors, in the presenceof at least one source of carbon in liquid, solid, gaseous orheterogeneous form. The source of carbon that is used is for example inthe form of particles of graphite in suspension in a hydrocarbon or in arefinery waste.

The process is advantageously carried out in the presence of a solventthat operates to disperse the precursors of the original mixture thatwill be subject to homogenization, and more particularly to prevent theformation of precursor agglomerates. This solvent is preferably of theorganic type and is preferably selected from the group consisting ofwater, organic solvents and inorganic solvents. Among the organicsolvents, alcohols, esters and ketones are preferred.

According to an advantageous embodiment of the invention, the source ofcarbon that is used for carrying out the process, is in liquid form andconsists of:

-   -   one or more hydrocarbons, preferably a mixture of hydrocarbons        in liquid form at room temperature, such as refinery wastes,        preferably petroleum coke or breakage coke; or    -   one or more polymers having a molecular weight higher than        50,000, preferably a mixture derived from or based on oxygenated        polymers such as a mixture of propylene oxide in acetonitrile.

According to an advantageous embodiment, the source of carbon in liquidform is selected from the group consisting of particles of synthetic ornatural carbon, such as particles of Ketjen black, Shawinigan black or amixture thereof.

Preferably, the source of carbon that is used in solid form has a puritygreater than 50% and the impurities, if any, are preferably selectedfrom the group consisting of sulfur, nitrogen and oxygen.

When the source of carbon is in gaseous form, it is selected from thegroup consisting of alkanes, alkenes, alkynes or a mixture thereof. Thegaseous source is preferably a gas such as CH₄, C₂H₆, C₂H₂ or a mixturethereof.

The process for preparing a ceramic powder according to the inventioncomprises at least one of the following steps:

-   -   a) homogenization, in the presence of the source of carbon and        eventually in the presence of a solvent, to obtain an intimate        mixture, preferably by grinding, more preferably by high energy        grinding, of a mixture of particles that can result in ceramics        by heat treatment;    -   b) removal of the solvent used; and    -   c) carbonization of the residual carbon that is present in the        mixture obtained in step a) or b) when the source of carbon does        not essentially consist of carbon, by heat treatment of said        intimate mixture obtained in step a) or b).

The removal of the solvent from the intimate mixture obtained in step a)is carried out at a temperature preferably between 40 and 150 degreesCelsius, more preferably at a temperature between 60 and 120 degreesCelsius.

Introduction of the source of carbon and of the solvent is preferablycarried out at the start of step a) but may also be carried out duringstep a).

By carrying out the process under a reducing atmosphere that ispreferably formed with nitrogen, argon or a mixture thereof, it ispossible to obtain particles of ceramic powder that are coated withcarbon.

Advantageously, the source of solid carbon consists of particles ofcarbon having a size that varies between 10 and 900 nanometers andhaving a specific surface measured according to the BET method that isgreater than 50 m²/g.

According to a particularly interesting embodiment of the process, themixture of particles capable of resulting in ceramics by heat treatmentis a mixture of particles of ZrO₂ and of particles of Y₂O₃. This mixturepreferably consists of x weight percent of particles of ZrO₂ and (100-x)weight percent of particles of Y₂O₃, where x varies from 1 to 99. Stillmore advantageously, x is close to 50.

According to another particular embodiment of the invention, the mixtureof particles capable of resulting in ceramics by heat treatment and thatis used for carrying out the process, consists of particles of Li₂CO₃and particles of TiO₂. This mixture consists of x weight percent ofparticles of Li₂CO₃ and (100-x) weight percent of particles of TiO₂,where x varies between 1 to 99. Even more advantageously, x is close to50.

According to another particular embodiment, the mixture of particlescapable of resulting in ceramics by heat treatment consists of particlesof Li₂CO₃ and particles of TiO₂. This mixture consists of x weightpercent of particles of Li₂CO₃ and (100-x) weight percent of particlesof TiO₂, where x varies between 1 to 92. In this case the source ofcarbon preferably consists of a polyoxyethylene based polymer. Thispolyoxyethylene preferably has an average molecular weight of 54,000 andis advantageously dissolved, before the homogenizing step, in a aqueousor organic solvent such as acetonitrile.

For carrying out the process, the particles of the mixture that canresult in ceramics preferably have a size between 1 nanometer and 10micrometers. This size is still more advantageously between 20 and 800nanometers.

Particularly advantageous results are obtained when carrying out thepreparation process with particles of ZrO₂, Y₂O₃, TiO₂ or Li₂TiO₃ whosesize varies between 1 and 10 microns.

Among carbon powders, those having a size distribution characterized bya D50 between 10 nanometers and 10 micrometers, more particularly thosehaving a D50 between 100 nanometers and 2 micrometers should beparticularly mentioned.

When the powder from the source of carbon consists of a polymer or ahydrocarbon in powder form, the corresponding powders with a D50 of 10to 500 nanometers, preferably those with a D50 that varies between 100and 200 nanometers are considered advantageous.

With respect to the particles of the source that can result in ceramicsby heat treatment, those having a size distribution characterized by aD50 between 10 nanometers and 10 micrometers are preferred. Those havinga D50 between 100 nanometers and 2 micrometers are particularlyinteresting.

Generally, interesting results are obtained when the various particlesused in the process have substantially similar granulometry, and moreparticularly those being characterized by D50 lower than or equal to 1micrometer.

When homogenization is carried in step a) of the process under dryconditions, an Aglomaster mixer of HOSOKAWA is preferably used. Whenhomogenization is carried out in step a) under wet conditions, amechano-fusion device of KOSOKAWA, Japan, is advantageously used.Particularly for mixers of the Aglomaster type the homogenization speedis preferably between 1500 and 3000 rpm.

Step a) generally lasts between 1 and 3 hours. Preferably step a) lastsabout 2 hours.

On the other hand, step c) lasts 2 to 24 hours. Preferably step c) lastsabout 3 hours.

According to an advantageous embodiment of the invention, the steps arecarried out under an inert atmosphere, in order that carbon remains inthe final product, preferably under nitrogen or argon, or under amixture thereof. Otherwise, carbon is oxidized and removed byevaporation, as carbon dioxide.

In the case where it is desired to remove any trace of residual carbonfrom the ceramic powder that is obtained at the end of the process, atleast one step of the process is then carried out in the presence of asource of oxygen such as air or pure oxygen. This precaution isnecessary in particular in the case where the presence of residualcarbon could be harmful to the quality of the ceramics that one intendsto prepare from this powder.

The source of carbon may in part be in liquid and/or gaseous form.

According to an advantageous embodiment of step b) removal of thesolvent is carried out at a temperature between 200 and 500 degreesCelsius, and more preferably at a temperature of about 400 Celsius. Thisheat treatment for its part advantageously lasts between 12 and 24hours, and preferably about 20 hours.

According to a preferred embodiment of the present invention, thecarbonization step is carried out in the reactor that was used to carryout homogenization of the mixture that can result in ceramics by heattreatment.

The preparation process according to the invention allows for example toobtain a ceramic powder whose particles have a size dimension between 10nanometers and 1 micron. The size of the particles of the ceramic powderobtained is advantageously between 50 and 500 nm.

In homogenization step a), the temperature is advantageously set between20 and 40° Celsius, more preferably this temperature is about 25° C.

In carbonizing step b), the temperature is advantageously set between700 and 1200° Celsius, more preferably this temperature is about 1100°C.

Advantageously, the amount of carbon source used in the processrepresents 2 to 10 weight percent, preferably 6 weight percent of themixture of particles that can result in a ceramic product by heattreatment.

Preferably, the source of carbon is a polymer and the amount of polymerused represents from 5 to 30 weight percent, preferably about 20 weightpercent, more preferably about 10 weight percent of the mixture ofparticles that can result in a ceramic product by heat treatment.

In the particular embodiment in which a powder mixture of Y₂O₃ and ZrO₂is used for the preparation of the ceramic powder, the quantity of Y₂O₃in the mixture of particles subjected to grinding varies between 5 and15% and the quantity of ZrO₂ varies between 5 to 15 weight percent.

The preparation process according to the present inventionadvantageously makes it possible to obtain a ceramic powder having atthe end of step b) or at the end of step c) a nano type structure, morepreferably the size of the ceramic particles thus obtained is between 10and 900 nanometers.

A second object of the present invention consists in ceramic powderscapable of being obtained by one of the processes that are the object ofthe present invention. These powders are for example characterized by ahomogenous size distribution and/or a residual carbon content of between0.05 and 10%.

A third object of the present invention consists in a process forpreparing a ceramic product including the steps of preparing a ceramicpowder, that are defined within the framework of the first object of theinvention as well as a final step in which the ceramic powder that isobtained is subjected to, according to a usual mode of transformation ofthe ceramic powders into a ceramic powder, at least one heat treatmentat a temperature higher than 800° Celsius, for a period of time that ispreferably comprised between 3 and 24 hours.

A fourth object of the present invention consists in a ceramic productcapable of being obtained by the process according to the third objectof the present invention. Among these ceramic products, those containingresidual carbon are particularly interesting for their conductivity.

A fifth object of the present invention is constituted by the use of apowder or a ceramic product according to the invention in the field offuel batteries or in the field of automobile, more particularly in thepreparation of piston heads.

These powders and ceramic products are also advantageously used for thepreparation of anodes or ceramic electrolytes and those deprived ofresidual carbon are advantageously used in the manufacture of electricinsulators.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The process for preparing a ceramic powder according to the presentinvention is advantageously carried out in two steps as illustrated inFIG. 2.

The first step for preparing a ceramic powder consists for example inpreparing a powder in the presence of carbon from a mixture preferablyof ZrO₂ and Y₂O₃, by high energy mechanical grinding preferably during 1to 2 hours, until the mixture becomes intimate.

The second step for preparing a ceramic product consists in heating apowder obtained in the first step, preferably at a temperature of 850°C., preferably during 3 hours. The ceramic powder thus obtained is ananometric powder. The formation of the ceramic product is confirmed byX ray diffraction.

This process is simple to operate due to the fact that it includes onlytwo steps, moreover these steps are short and require only a smallenergy input. Finally, another advantage, the nano form is obtainedafter only 5 hours.

Moreover, the energy required for the manufacture of a ceramic powder isnegligible, i.e. about 17 KWh, as illustrated in FIG. 2 annexed hereto.

The process for preparing a ceramic product according to the presentinvention includes a step of producing the ceramic product during whichthe ceramic powder obtained is heat treated at a temperature higher than800° C.

EXAMPLES

The following examples are given purely by way of illustration andshould not be interpreted as constituting any limitation of theinvention.

Conventional Process for Preparing a Ceramic Product

FIG. 1 annexed hereto illustrates one of these processes ofmanufacturing a ceramic product in a plurality of grinding and heattreatment steps. The duration of such a process is about 150 hours, theenergy used for the preparation of about 1 kg of ceramic product is ofthe order of 600 kWh, which involves non-negligible production costs.

Example 1 Dry Preparation of a Ceramic Powder Comprising Particles ofLiTi₂O₄ Coated with Carbon

Preliminary Step of Preparing a Powder of Li₂TiO₃

This step consists in mixing 20 grams of a TiO₂ powder of a particlesize of 20 nanometers, with anatase structure (from Kronoss, inVarennes—Canada) with 18.5 g of a Li₂CO₃ powder of a particle size of500 nanometers (marketed by Aldrich, Canada).

After an intimate homogenization by co-grinding during 1 hour, a powderwith fine grading is obtained. This co-grinding is carried out byheating in two consecutive steps, at 400° C., then at 750° C.,respectively during 1 and 10 hours. A product (A) consisting of Li₂TiO₃of stoichiometric structure is then obtained.

Preparation of LiTi₂O₄

In this second step, a mixture (B) consisting of 10 grams of product (A)of formula Li₂TiO₃, obtained in the preliminary step, is mixed with 10.8grams of TiO₂, 19.4 grams of Ti₂O₃ (Aldrich, Canada) and 2.4 grams ofShawinigan carbon black.

After an intimate grinding during 1 hour at room temperature, a finegrading powder is obtained. The mixture obtained is again reheated underargon during 15 hours.

The final product is a ceramic powder of a LiTi₂O₄ type structure.

Example 2 Dry Preparation of LiTi₂O₄ Particles Coated with a PolymerInduced Carbon

This preparation is carried out similarly as in example 1, except thatthe source of solid carbon is replaced by a POE based polymer, i.e. by apolyoxyethylene of average molecular weight 900,000. The polymer isdissolved in an excess of water and then mixed with composition (B)without carbon.

The weights of the different powders used are the same as in example 1and the weight of the polymer is 25 grams. The mixture is first dried at120° C. during 24 hours. After an intimate grinding during 1 hour, apowder with fine grading is obtained. The mixture obtained is againreheated under argon during 15 hours. The final product has a LiTi₂O₃type structure.

Example 3 Preparation of Ceramic Products

By heating the ceramic powders obtained in examples 1 and 2, at atemperature higher than 750 degrees Celsius and during more than 15hours, a ceramic product is obtained.

Although the present invention has been described by means of specificembodiments, it is understood that many variations and modifications maybe associated with said embodiments, and the present invention aims atcovering such modifications, uses or adaptations of the presentinvention following in general, the principles of the invention andincluding any variation of the present description that will becomeknown or conventional in the field of activity of the present invention,and that may apply to the essential elements mentioned above, inaccordance with the scope of the following claims.

The invention claimed is:
 1. A process for the preparation of a ceramicproduct, said process comprising: preparing a ceramic powder; andsubjecting the ceramic powder to at least one heat treatment at atemperature higher than 800° C., wherein the ceramic powder is preparedfrom a mixture of precursors of said powder and in the presence of atleast one source of carbon by a method comprising the following steps:a) homogenization, in the presence of the source of carbon andoptionally in the presence of a solvent, to obtain an intimate mixtureof precursor particles that can result in a ceramic product by heattreatment; and b) removal of the solvent eventually if present in theintimate mixture obtained in step a); wherein the source of carbon isselected from the group consisting of liquid forms, gaseous forms andmixtures thereof; and wherein the homogenization step a) is carried outby high-energy grinding.
 2. A process for the preparation of a ceramicproduct, said process comprising: preparing a ceramic powder; andsubjecting the ceramic powder to at least one heat treatment at atemperature higher than 800° C., wherein the ceramic powder is preparedfrom a mixture of precursors of said powder and in the presence of atleast one source of carbon by a method comprising the following steps:a) homogenization, in the presence of the source of carbon andoptionally in the presence of a solvent, to obtain an intimate mixtureof precursor particles that can result in a ceramic product by heattreatment; and b) removal of the solvent eventually if present in theintimate mixture obtained in step a); wherein the source of carbon isselected from the group consisting of liquid forms, gaseous forms andmixtures thereof; and wherein the homogenization step a) is carried outby mechanofusion.
 3. A process for the preparation of a ceramic product,said process comprising: preparing a ceramic powder; and subjecting theceramic powder to at least one heat treatment at a temperature higherthan 800° C., wherein the ceramic powder is prepared from a mixture ofprecursors of said powder and in the presence of at least one source ofcarbon by a method comprising the following steps: a) homogenization, inthe presence of the source of carbon and optionally in the presence of asolvent, to obtain an intimate mixture of precursor particles that canresult in a ceramic product by heat treatment; and b) removal of thesolvent eventually if present in the intimate mixture obtained in stepa); wherein the source of carbon is selected from the group consistingof liquid forms, gaseous forms and mixtures thereof; wherein thehomogenization step a) is carried out by high-energy grinding; andwherein the intimate mixture of particles that can result in the ceramicproduct by heat treatment is a mixture of: 1) particles of ZrO₂ andparticles of Y₂O; or 2) particles of Li₂TiO₃ and of particles of TiO₂.4. The process of preparation according to claim 1, wherein the sourceof carbon is selected from the group consisting of Ketjen black,Shawinigan black, CH₄, C₂H₆, C₂H₂ and mixtures thereof.
 5. The processof preparation according to claim 1, wherein a temperature during theremoval step b) is between 40 and 150° C.
 6. The process of preparationaccording to claim 1, wherein the source of carbon and the solvent areintroduced during step a).
 7. The process of preparation according toclaim 1, carried out at least partially under a reducing atmosphere,said reducing atmosphere preventing transformation of the carbon, thatis present in the reaction mixture, into carbon dioxide, and allowing toobtain particles of ceramic powder that are coated with carbon.
 8. Theprocess of preparation according to claim 1, wherein step a) lastsbetween 1 and 3 hours.
 9. The process of preparation according to claim1, wherein at least one of the steps is carried out under inertatmosphere.
 10. The process of preparation according to claim 1, whereinat least one step of the process is carried out in the presence of asource of oxygen, in order to remove any trace of residual carbon fromthe ceramic powder obtained at the end of the process.
 11. The processof preparation according to claim 2, wherein the source of carbon isselected from the group consisting of Ketjen black, Shawinigan black,CH₄, C₂H₆, C₂H₂ and mixtures thereof.
 12. The process of preparationaccording to claim 2, wherein a temperature during the removal step b)is between 40 and 150° C.
 13. The process of preparation according toclaim 2, wherein the source of carbon and the solvent are introducedduring step a).
 14. The process of preparation according to claim 2,carried out at least partially under a reducing atmosphere, saidreducing atmosphere preventing transformation of the carbon, that ispresent in the reaction mixture, into carbon dioxide, and allowing toobtain particles of ceramic powder that are coated with carbon.
 15. Theprocess of preparation according to claim 2, wherein step a) lastsbetween 1 and 3 hours.
 16. The process of preparation according to claim2, wherein at least one of the steps is carried out under inertatmosphere.
 17. The process of preparation according to claim 2, whereinat least one step of the process is carried out in the presence of asource of oxygen, in order to remove any trace of residual carbon fromthe ceramic powder obtained at the end of the process.
 18. The processof preparation according to claim 3, wherein the source of carbon isselected from the group consisting of Ketjen black, Shawinigan black,CH₄, C₂H₆, C₂H₂ and mixtures thereof.
 19. The process of preparationaccording to claim 3, wherein a temperature during the removal step b)is between 40 and 150° C.
 20. The process of preparation according toclaim 3, wherein the source of carbon and the solvent are introducedduring step a).
 21. The process of preparation according to claim 3,carried out at least partially under a reducing atmosphere, saidreducing atmosphere preventing transformation of the carbon, that ispresent in the reaction mixture, into carbon dioxide, and allowing toobtain particles of ceramic powder that are coated with carbon.
 22. Theprocess of preparation according to claim 3, wherein step a) lastsbetween 1 and 3 hours.
 23. The process of preparation according to claim3, wherein at least one of the steps is carried out under inertatmosphere.
 24. The process of preparation according to claim 3, whereinat least one step of the process is carried out in the presence of asource of oxygen, in order to remove any trace of residual carbon fromthe ceramic powder obtained at the end of the process.
 25. The processof preparation according to claim 3, wherein the particles of ZrO₂ andY₂O or the particles of Li₂TiO₃ and TiO₂ have a size that varies between1 and 10 microns.
 26. The process of preparation according to claim 3,wherein a quantity of Y₂O₃ in the mixture of particles subject togrinding varies between 5 and 15 weight percent and a quantity of ZrO₂varies between 5 and 15 weight percent.
 27. The process of preparationaccording to claim 3, wherein the mixture of particles of ZrO₂ and Y₂O₃is a mixture consisting of x weight percent of particles of ZrO₂ and(100-x) weight percent of particles of Y₂O₃, where x varies from 1 to99; or wherein the mixture is a mixture consisting of x weight percentof particles of Li₂TiO₃ and (100-x) weight percent of particles of TiO₂,where x varies from 1 to
 99. 28. The process of preparation according toclaim 27, wherein x is close to
 50. 29. The process of preparationaccording to claim 1, wherein the homogenization is carried out in stepa) with or in a solvent by means of a mechano-fusion device.